Communication systems typically include a plurality of dispatch consoles and communication units, such as mobile or portable radio units, that are geographically distributed among various base sites and console sites. The communication units wirelessly communicate with the base sites and each other, and are often logically divided into various talkgroups. Communication systems may be organized as trunked systems, where a plurality of radio frequency (RF) communication resources are allocated amongst multiple users or groups by assigning the base sites within a coverage area on a call-by-call basis, or as conventional (non-trunked) systems where RF communication resources are dedicated to one or more users or groups. In trunked systems, or in mixed trunked and conventional systems, there is usually provided a central controller/server (sometimes called a “zone controller”) for allocating RF communication resources among a group of sites.
Many such communication systems use Internet Protocol (IP) to transport packet data representative of voice, video, data or control traffic between endpoints (or “hosts” in IP terminology). In such systems, host devices, including base stations, consoles, zone controllers, and in some instances, wireless mobile or portable radio units in different zones, are logically interconnected by various routers forming an IP network. Data is divided into IP packets called datagrams, which include addressing information (e.g., source and destination addresses) that enables the routers of the network to transport the packets to the specified destination(s).
Typically, systems utilizing IP to transport packet data include various congestion control protocols. For example, one well known congestion protocol, commonly referred to as explicit congestion notification (ECN) marking, is described in U.S. patent Pub. Ser. No. 2006/0015639. In systems utilizing ECN marking, exit routers for each of the zones in a communication system assess the availability of inter-zone resources in the IP network and update an ECN field in transmitted control packets to indicate the level of congestion.
However, many communication systems today also make use of an external packet switched network, such as Multi-Protocol Label Switching (MPLS), to reduce costs by reusing network infrastructure and bandwidth used by other types of networked systems. Such external packet switched networks typically do not provide any congestion notification or avoidance mechanisms appropriate for real-time voice applications. As a result, congestion within the external packet switched network cannot be readily detected by many communications systems, resulting in dropped packets when such congestion is present.
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